The present invention relates to a clamping mechanism for clamping an information recording disk such as a compact disk to a turntable during the reproduction of the disk.
Conventionally there has been employed a clamping mechanism of the type shown in FIGS. 1 through 3 of the attached drawings. In these drawings, an information recording disk A, such as a compact disk, has a center hole B. A spindle motor C rotates a spindle D to which a turntable E is fixed.
A centering member F for centering the information recording disk A has a central portion slidably mounted on the spindle D within the turntable E, and an outer circumferential portion in the form of a tapered portion G which can fit within an inner circumferential edge of the center hole of the disk A. The centering member F is urged upward by a compression spring H provided between the centering member F and the turntable C. A magnetic stopper I fixed on the upper end of a column portion of the turntable E prevents the centering member from coming off the spindle D.
A clamper J is provided for pressing and clamping the information recording disk A against the disk carrying surface of the turntable E. As shown in FIGS. 4 through 7, the clamper J is constituted by a pressing member K formed in the shape of an inverted saucer and a ring-like magnet L fixed to the center of the lower surface of the pressing member K. A ring-like pressing member M, which is adapted to be brought into contact with the information disk A, is formed on the outer circumference of the lower surface of the pressing member K, and a shaft hole N into which the spindle D can be inserted is formed in the central portion of the pressing member M. A saucer-like engagement/stopper member O is fixed on the upper surface of the pressing member K, and a circumferential engagement/stopper groove P is formed in the outer circumference between the engagement/stopper member O and the upper surface of the pressing member K. A retaining pawl Q, which is fixed to a vertically movable holder (not shown), engages the circumferential engagement/stopper groove P so that the clamper J is rotatably retained by the holder.
During reproduction, when the information recording disk A is mounted on the disk carrying surface of the turntable E, the center hole B of the disk A fits with the tapered portion G of the centering member F so that the disk A is centered relative to the spindle D. When the clamper J is then lowered by the holder, the magnet L of the clamper J is attracted to the stopper I of the turntable E so that the attraction force acts in such a manner that the pressing member M of the pressing member K of the clamper J urges the information recording disk A against the turntable E, and at the same time the top end portion of the spindle D rotatably fits into the shaft hole N of the clamper J. When the turntable E is then rotated by the spindle motor C, the clamper J rotates together with the information recording disk A.
FIG. 8 shows another conventional clamper J in which clamp shafts S are vertically movably disposed at predetermined circumferential intervals along a circle on a disk retaining member R, and coil springs T urge the respective clamp shafts S downward.
In this case, when a magnet L of the clamper J is attracted to a turntable E, the lower end portions of the clamp shafts S are raised by the attractive force against the elastic force of the respective coil springs T so that an information recording disk is pressed and clamped against the turntable E by the recovery force of the coil springs T.
In the former clamp device, however, there have been various drawbacks in that when the thickness of the information recording disk varies as shown in FIGS. 1 through 3, the gap between the surface of the turntable E and the magnet L varies, whereby the clamping force varies with the variations in the thickness of the disk, making the clamping operation unstable.
In the latter conventional clamp mechanism, on the other hand, while the variations in the clamping force can be eliminated, additional components such as the clamp shafts S and the coil springs T are required, making the total number of parts large. Also, it is necessary to provide space for arranging the clamp shafts S, etc., making the saucer-like retaining member R large in size. Furthermore, because the clamper has sliding portions in the form of the clamp shafts, there are further disadvantages in that the performance of the mechanism tends to deteriorate over time and highly precise components are required.